a) Field of the Invention
The present invention relates to a separate head-up display device and, more particularly, to a head-up display device for removing shakes and easily adjusting a direction of a reflective sheet, so that a driver may easily adjust the direction of the reflective sheet to obtain an optimal viewing angle, to thereby improve driving safety.
b) Description of Prior Art
There are more and more information in vehicles, accidents may happen if drivers moves line of sight from the road during driving. A head-up display device is provided for drivers to see the road ahead simultaneously during reading information, especially a head-up display device using a concave mirror to form a virtual image, which may be provided to enlarge the displayed area and the distance of the displayed image is enough, usually larger than 2 meters, so that drivers' focal length of reading displayed information is similar to focal length of watching road condition ahead, therefore drivers may take care the road condition during reading information, dangerous of driving may be greatly reduced.
The principle of virtual imaging applied in head-up display device is that a concave mirror is used for imaging. Concave mirror imaging equation is: 1/p+1/q=1/f; wherein f: focal length, q: object distance, p: image distance. Under a general magnification, virtual images may be enlarged, and the distance of the virtual image may become far at the same ratio. The best ratio for readers is about 4 to 6 times, readers may easily feel dizzy if magnification is too large. If we want the distance between the virtual image and driver's eyes larger than 2 meters, image may be formed in rear of the reflective sheet about 1.2 meters, it means that the optical distance from the display to the concave mirror is larger than 24 cm (if the magnification is five times). The distance of light path could be increased by multiple reflections back and forth between mirrors, but the volume needed by the light path is large. Usually, a space is special arranged inside the dashboard for installing a head-up display device.
The related technology may be referred to the cited references TW patent no. M426681, M463217, M525111, M439181, M464668, M468454, 1326652 and TW publication no. 201122548, 201144861, 201400329. Use of technology of head-up display devices has already disclosed in the cited references, but the following drawbacks are existed in use commonly:
1. For after market, the space on the dashboard is not enough for installing the head-up display device because the volume needed by the light path is too large that may obstruct the line of sight of drivers.
2. For solving the problem that the volume needed by the light path is too large, another method is using a separate way for this structure, namely, the display screen is fixed on an upper portion of the windshield and the reflective sheet is fixed on the dashboard. However, in many vehicles, the dashboard may shake due to operation of an engine or an air-conditioning compressor, this kind of shake may let the reflective sheet fixed above shake together, and displacement of shakes may be enlarged at the magnification due to the magnification effect of the concave mirror, so that the display screen may be shaken severely.